1. Field of the Invention
The present invention relates to a method of manufacturing Perovskite dielectric film which has outstanding dielectric and pyroelectric characteristics and is widely used for making capacitors and infrared sensors for example.
2. Description of the Prior Art
Owing to outstanding dielectric and pyroelectric characteristic, Perovskite-type dielectric material is widely used for a variety of industrial requirements.
Because of very high resistivity and dielectric constant, barium titanate BaTiO.sub.3 is widely used for making ceramic filters and highly-dielectric capacitors. On the other hand, ceramics made from strontium titanate SrTiO.sub.3 is mainly used for making power-supply capacitors due to less depending on the voltage in the presence of high voltage, although the dielectric constant is lower than that of the barium titanate. Magnesium titanate MgTiO.sub.3 and calcium titanate CaTiO.sub.3 feature outstanding temperature characteristics of dielectric constant and minimum dielectric loss factor. In particular, since magnesium titanate has the positive value of temperature coefficient of dielectric constant and calcium titanate has the negative value, both the dielectric constant and temperature coefficient of the dielectric constant are freely variable by manufacturing the blends (Mg, Ca)TiO.sub.3. Owing to this advantage, the blend material is widely used for manufacturing temperature-compensative capacitors in a substantial volume. On the other hand, due to outstanding pyroelectric characteristics, lead titanate PbTiO.sub.3 is widely used for making pyroelectric infrared sensors.
Recently, there is a positive movement among the concerned to make more compact and light-weight electronic parts. They positively follow up research on the effective application of thin film made from dielectric material to the production of compact capacitors having large capacity and monolithic sensors incorporating either field-effect transistors (FET) or bipolar transistors installed on the identical substrate.
Actually, there are few reports on the production of thin film made from strontium titanate, magnesium titanate, and calcium titanate. Conversely, there are a number of reports on the production of thin film made from barium titanate and lead titanate.
Study on the production of barium titanate during the past years was based on the vacuum evaporation process like the one announced by C. Feldman, Rev. Sci. Inst., 26, 463 (1955) and A. E. Feuersanger, J. Electrochem. Soc., 111, 1387 (1964) for example.
Nevertheless, when producing complex oxide like barium titanate for example, since the speeds of evaporating barium and titanium from the evaporation source are different from each other, their mol ratio cannot properly be controlled. Furthermore, since barium titanate has a very high melting point, heater material is necessarily blended with barium titanate, thus generating disadvantage. To solve this problem, recently, those who skilled in the art mostly follow up study on the production of barium titanate film by applying a RF-sputtering process using barium-titanate ceramic sheet as target. This process yields barium titanate film having a minimum of dielectric constant 1,000. This was reported by T. L. Rose, E. M. Kelliher, A. N. Scoville, and S. E. Stone, J. Appl. Phys., 55, 37.06 (1984) for example.
On the other hand, when producing barium titanate film based on the conventional RF-sputtering process, in order to make such barium titanate having a minimum of dielectric constant 1,000, a minimum of 900.degree. C. of the substrate temperature or heating temperature is needed for securely forming thin film. In many cases, as a result of heat treatment with extremely high temperature and due to the growth of crystalline granules, either microscopic cracks or pin holes are generated. As a result, after formation of electrodes by evaporation, short-circuit is likely to be generated.
Likewise, a variety of trials were carried out for producing thin film made from lead titanate. Actually, those infrared sensors composed of poly-crystalline film of lead titanate were experimentally produced, where the produced film had such physical characteristics close to those of the bulk material. This was reported by M. Okuyama et al., in Jpn J. Appl. Phys. 22, Suppl. 21-1, 465 (1983) for example.
Furthermore, in order to effectively utilize the physical property of lead titanate which generates spontaneous polarization in the direction of the axis C, such an epitaxial film oriented in the direction of the axis C is produced. The produced film is provided with outstanding pyroelectric characteristics which triples the proper pyroelectric characteristics of bulk material. This was reported by R. Takayama et al., in Jpn. J. Appl. Phys., 61, 411 (1987).
Nevertheless, when producing thin film by means of the RF-sputtering process, film cannot be formed very quickly, and yet, since the sputtering rate varies according to the kinds of elements blended in the complex oxide, it is still difficult to properly control the structure of the formed film based on the stoichiometry. To overcome those problems, trials are underway for producing lead-titanate film based on the MO-CVD method which is capable of minimizing such defect mentioned above. As a result, such an epitaxial film oriented in the direction of the axis C has already been produced at a very fast depositing speed which is extremely faster than the RF-sputtering process at 500.degree. C. through a maximum of 600.degree. C. of the substrate temperature. This was reported by M. Okada et al., in J. Ceram. Soc. Jpn., 96, 687 (1988).
Nevertheless, in order to properly yield lead-titanate film oriented in the direction of the axis C by applying either the RF-sputtering or the MO-CVD process, it is essential for the system to heat the substrate to a minimum of 500.degree. C.